The present invention relates to improvements in blast pipes for use in metallurgical converters.
Quite often metallurgical converters are provided with double or triple blast pipes, that is to say, with two or three concentric tubes, which are protected while in service against wear. The tubes when hot, are acted upon by a liquid or gaseous protective fluid fed to the outer tube. In the majority of cases this protective fluid consists of a hydrocarbon, either as a liquid such as, a fuel-oil or as a gas such, propane, butane, natural gas, etc. These blast pipes are often arranged in the bottom of the converter.
Such a known blast pipe for refinement of the metal bath may also, if the case arises, function as a burner, since it can simultaneously introduce fuel on one hand and a fluid to complete combustion.
However, such a blast pipe is a poor burner because a heavy flow of fluid for completing combustion passes through the central tube and exits at high speed from the nose of the blast pipe, causing a small flow of fuel to pass out the sides of the blast pipe. In other words, mixing of fuel and fluid for completing combustion is very poor and combustion is not satisfactory.
The principal features of the invention relate to a blast pipe for a metallurgical converter comprising a plurality of concentric tubes, the cross-sections of said tubes being adapted to the fluid flows required for the refining of a metal bath. The first outermost tube is fed with a combustible fluid, wherein the second tube, adjacent said first tube, defines on the inside, an annular combustible fluid passage for the passage of gas to complete combustion. The second tube extends beyond said first tube at the end of the blast pipe, and is provided with a row of orifices solely in the projecting portion of the second tube. The end portion of the second tube is closed by a metal cap soldered thereto said end by a hard solder which melts at a predetermined temperature.
The orifices in said second tube preferably all have the same dimensions, are uniformly spaced, have a circular shape or provided with longitudinal slits or the like.
The metal constituting the hard solder of the cap is preferably a metal or alloy, the melting point of which lies between 400.degree. C. and 1200.degree. C., depending on the nature of the metal bath to be refined. The metal cap may be of steel (thin sheet) or of a non-ferrous metal.
As will be understood, a blast pipe as above described initially constitutes a burner which can be employed for heating or firing the refractory lining of a metallurgical converter. As soon as the liquid metal is poured into the converter for refining the hard solder fixing the cap so as to close the end of the second tube, melts under the effect of the radiant heat; the refining fluid or fluids then pass into the converter whilst the peripheral fluid protects the blast pipe against wear. In other words, the blast pipe then functions as a blast pipe for refining and no longer as a burner, because the projecting portion of the second tube provided with orifices gets worn away quickly. This transformation from burner to blast pipe for refining is irreversible. But this is not undesirable since it is the lining in the new state which needs to be heated and fired.